Weather radars are used to detect the intensity of echoes reflected from precipitation particles of clouds, rain and the like, and to observe or forecast the state of weather. Recently, Doppler radars capable of detecting dynamic change of rain and clouds using the Doppler effect of reflected waves, have been used as weather radars.
When an observation target is close to a radar, the reception frequency becomes high because of the Doppler effect, and when an observation target is away from the radar, on the other hand, the reception frequency becomes low. Using the Doppler effect, Doppler radars detect the moving speed of an observation target based on frequency variation of received waves. More specifically, Doppler radars receive reflected pulses reflected by an observation target, and detect the Doppler velocity based on the amount of phase variation between the pulse hits.
In the case of observation using Doppler radars, signals from other radar sites, for example, may be mixed to the received signals as interference waves. It is also possible that multipath interference occurs and unnecessary signals are mixed to the received signals. As a technique of removing such interference waves, “Meteorological Agency, ‘Doppler Radar for Airport Weather Manufacturing Specification (Kagoshima Airport)’, May 2006, p. 19” discloses a technique of replacing IQ data judged as including interference waves with IQ data of a hit before.